Air conditioning system fault diagnosis guide (part 2)

Air conditioning system fault diagnosis guide (part 2)

This article continues from the previous article: A Guide to Fault Diagnosis of Air Conditioning System (Part 1) During the intense heat, air-conditioning maintains the "life" of some people. People are afraid of heat that they can't live without air-conditioning.

However, if the air conditioner is used for a long time, there will be many failures, so many customers leave messages to us in the background: the air conditioner is wattage, not cooling, the system is abnormal, it is not as good as before... etc. What to do if the air conditioning system fails? Overhaul is the key As we all know, when facing air conditioning system troubleshooting, the first step is how to accurately and quickly detect the source of the air conditioning system failure? In the previous "Air-conditioning System Fault Diagnosis Guide-Part 1", the editor mentioned various faults in the air-conditioning system, such as "abnormal low pressure and high pressure values ​​of the refrigeration system", "abnormal temperature changes in the compressor casing", and "temperature difference between air inlet and outlet" Value is abnormal", "The temperature of the air outlet of the air conditioner is too high or low"... and other problems, the okmarts.com application engineer is specially invited to give an explanation of measurement parameters, measurement instruments and connection methods, and system testing points. Analysis of big technical dry goods, readers who have read this guide (Part 1) have left messages to benefit a lot and increase their knowledge, urging the editor to hurry up to the next part of this guide. Therefore, today, our encyclopedia platform still invites okmarts.com application engineers to continue to explain for us the "Air-conditioning System Fault Diagnosis Guide-Part Two" about: using parameters to comprehensively determine the system failure and the normal range of operating parameters and other two knowledge points. 　 1. Comprehensively judge system faults with the help of parameters In a guide, I know that a large number of coefficients (such as: "evaporation pressure, condensation pressure, saturated evaporation temperature, saturated condensation temperature, superheat, subcooling") are often used as a reference when judging air conditioning system failures. Before checking the system parameters, what should we pay attention to? The okmarts.com application engineer summarized the following precautions for us: 1. Make sure all filters, fans and coils are clean 2. Confirm the throttle and refrigerant type 3. Ensure that the air volume of the indoor air outlet is in the normal range 4. For the heat pump system, test in the cooling mode

At the same time, he remarked the following 4 main points after the precautions to help operators improve work efficiency in a comprehensive and effective manner: 1) When the refrigerant charge is slightly insufficient, the system superheat and evaporation pressure may remain normal, but when the charge is severely insufficient, the pipeline may be frosted. 2) The pressure will quickly balance out during the shutdown period. 3) As flash gas enters the thermal expansion valve, or when the system load is low, the expansion valve may control the load. 4) It may be normal when the system refrigerant is overcharged. 2. Normal range of operating parameters The above is for the fault judgment when the operating parameters are abnormal. If the operating parameters are within the normal range, how to make accurate judgments for the capillary system and the thermal expansion valve (TXV) system? For capillary system: The okmarts.com application engineer suggested that the maintenance personnel must find the best superheat table, or calculate the best superheat table through the okmarts.com electronic refrigerant meter testo 550/557 smart App (as shown below). Figure 5 The okmarts.com electronic refrigerant meter set has the highest accuracy in the field of refrigeration measurement, and its performance far exceeds the analog refrigerant meter set. At the same time, the okmarts.com electronic refrigerant meter group can also detect the air tightness of the pipeline, detect even the smallest leaks, and stably record the vacuum process of the system. At the same time, okmarts.com application engineers remind everyone that the subcooling degree will change with the change of the system load, for example: when the outdoor temperature is 35°C, the nominal subcooling degree is 10°C. For thermal expansion valve (TXV) system The application engineer of okmarts.com emphasized that the subcooling degree required for the detection of thermal expansion valve (TXV) systems is generally 8~12℃. Here is the recommended electronic refrigerant meter series of okmarts.com, because the instrument is built with more than 60 common refrigerants The pressure-temperature characteristic curve can be easily applied to systems using different types of refrigerants. You can clearly see the convenient connection between the instrument and the system, simple operation, intelligent detection, and fast and accurate results.

At the same time, according to the application engineer of okmarts.com, the actual superheat at the low-pressure side inspection valve is 8~20℃, and the superheat at the evaporator outlet is 6~12℃. Finally, I believe that everyone has a more comprehensive understanding of the detection of air-conditioning system failures under the guidance of the application engineers of okmarts.com after reading the first and second chapters of the "Guide to Fault Diagnosis of Air-Conditioning System". If you have any questions, please leave a message at the bottom of our text.

Piston refrigeration compressor

The structure of the piston refrigeration compressor

Piston refrigeration compressor is mainly composed of three parts: working chamber part, machine base part and auxiliary system lubrication, cooling, etc.

The structure of the piston refrigeration compressor: the compressor is mainly composed of body, crankshaft, connecting rod, piston group, valve (valve), shaft seal, oil pump, energy regulating device, oil circulation system and other components.

Body:

Including two parts, cylinder block and crankcase, generally made of high-strength gray cast iron as a whole.



cylinder:

The cylinder is the main part of the working parts of the piston refrigeration compressor. According to the compressor's different pressure, displacement, gas properties and other needs, different materials and structural types should be selected. The basic requirements are: it should have sufficient strength and rigidity; it should have good cooling, lubrication and wear resistance.

Installation method of cylinder head:

1. From the middle to both sides; 2. Diagonally; 3. Divide two to three times; 4. Tighten according to the specified torque.



Crankshaft:

The crankshaft is one of the main components of the piston refrigeration compressor, which transmits the full power of the compressor. Its main function is to change the rotary motion of the motor into the reciprocating linear motion of the piston through the connecting rod.

link:

The connecting rod is the connecting piece between the crankshaft and the piston, which converts the rotary motion of the crankshaft into the reciprocating motion of the piston, and transmits the power to the piston to perform work on the gas. The connecting rod includes a connecting rod body, a connecting rod small end bushing, a connecting rod big end bearing bush and a connecting rod bolt.

Piston group:

Piston group is the general term for piston, piston pin and piston ring. Driven by the connecting rod, the piston assembly makes a reciprocating linear motion in the cylinder, thereby forming a variable working volume with the cylinder to realize the processes of suction, compression, and exhaust.

Pistons---Pistons can be divided into two categories: cylindrical and disc. The material of the piston is generally aluminum alloy or cast iron.

Piston pin---Piston pin is a part used to connect the piston and the small end of the connecting rod, and bears complex alternating loads during work.

Piston ring --- is a circular ring with an incision on the circumference of the ring. The incision is in the form of straight, oblique, and overlapping. The slope of the bevel is 45 degrees.

The piston ring includes a gas ring and an oil ring. The main function of the steam ring is to form a seal between the piston and the cylinder wall to prevent the compressed air from leaking from the gap between the piston and the cylinder wall; the function of the oil ring is to distribute oil and scrape excess lubricating oil on the cylinder wall.

Shaft seal---The function of the shaft seal is to prevent the compressed gas from leaking out along the extension end of the crankshaft, or to prevent the leakage of outside air when the pressure in the crankcase is lower than the atmospheric pressure.

Crankcase heater:

Separate the refrigerant in the crankcase to ensure the normal lubrication of the compressor. Any environment needs to install a crankcase heater. The crankcase temperature is higher than the ambient temperature by more than 20°C. The compressor is running, the crankshaft heater is powered off, the compressor is stopped, and the heater is powered on.



Protection device of compressor motor:

To prevent the compressor from overloading or overheating, the motor has 6 built-in PTC thermistors. Generally speaking, L and N are power supplies, and 11 and 14 are connected to the control circuit. 12 is an alarm indicator.

Oil pressure safety protection device:

Monitor the pressure difference between the inlet and outlet of the oil pump to ensure compressor lubrication. Generally it is less than 0.7bar, with a delay of 90±10 seconds. The oil pressure difference of the compressor is 2.5~3kg/cm.

The oil pressure difference of a single-stage compressor is: ΔP = oil pump outlet pressure-suction pressure



The oil pressure difference of the two-stage compressor is: ΔP = oil pump outlet pressure-intermediate pressure

Six systems:

(1) Motion system: crankshaft, piston connecting rod assembly, coupling, etc.;

(2) Air distribution system: valve plate, valve spring, etc.;

(3) Sealing system: piston ring, oil seal, gasket, packing, etc.;

(4) Body system: crankcase, cylinder block, cylinder liner, cover plate, etc.;

(5) Lubrication system: lubricating oil pump, oil filter, pressure regulating valve, etc.;

(6) Safety and energy regulation systems: safety valves, energy regulation devices, etc.

Other refrigeration components---oil separator:

Function: Separate the refrigerating oil in the refrigerant on the exhaust pipe to directly enter the crankcase of the compressor, reducing the amount of oil entering the refrigeration system.



Application: refrigeration systems with medium and low temperature ranges and long pipelines (liquid supply pipe, suction pipe).

Note: If the oil return of the system is not good, the refueling separator can only extend the operating time of the compressor and cannot solve the oil return problem of the system.,,,,



If the air-cooled condenser is higher than the compressor, (split unit, the air-cooled condenser is higher than> 1m), a check valve must be installed at the oil separator outlet to prevent the refrigerant from entering the oil separator when the system is shut down. Damage to the compressor.

Other refrigeration components---gas-liquid separator:

Function: Separate the non-evaporated refrigerant liquid in the refrigeration system before the compressor suctions to prevent the compressor from generating wet stroke (liquid hammer).



Application: medium and low temperature conditions.

Other refrigeration components---filter drier:

Function: Absorb and filter the moisture in the liquid refrigerant and filter the dirt and impurities in the refrigerant. It is generally installed at the refrigerant outlet of the accumulator and water-cooled condenser.

Other refrigeration components---solenoid valve:

Function: When the compressor stops running, the solenoid valve is closed to prevent the high pressure refrigerant from entering the low and low pressure system. Prevent liquid shock when the compressor restarts.



Installation position: 100mm～200mm away from the thermal expansion valve

Other refrigeration components---thermal expansion valve:

Function: throttling, reducing pressure. Installation location: The closer to the evaporator, the better.



The main features of piston refrigeration compressors:

advantage:

1) The applicable pressure range is wide, and the required pressure can be reached regardless of the flow rate;

2) High thermal efficiency and low unit power consumption;

3) Strong adaptability, that is, a wide exhaust range, which can adapt to a wide pressure range and cooling capacity requirements;

4) Strong maintainability;

5) Low material requirements, easier processing, and lower cost;

6) The technology is relatively mature and rich experience in production and use has been accumulated;

7) The installation system is relatively simple;

Disadvantages:

1) The speed is not high, the machine is big and heavy;

2) There are many wearing parts and a large amount of maintenance;

3) The exhaust is not continuous, causing air flow pulsation;

4) There is greater vibration during operation. Piston compressors have become the most widely used type and the largest production batch of refrigerators in various applications, especially in the small and medium refrigeration range.